Turbo machines having adjustable guide blades



Dec. 15, 1959 s. H. A. MAGIN 2,917,275

TURBO MACHINES HAVING ADJUSTABLE GUIDE BLADES Filed Oct. 2, 1953 2 Sheets-Sheet 1 Ihventor Attorneys TURBO MACHINES HAVING ADJUSTABLE GUIDE BLADES Filed Oct. 2, 1953 Dec. 15, 1959 s. H. A. MAGIN 2 Sheets-Sheet 2 Inventor A ltorney 5 United States Patent i TURBO MACHINES HAVING ADJUSTABLE GUIDE BLADES Sidney Henry Albert Magin, London, England, assignor to D. Napier & Son Limited, London, England, a British company Application October 2, 1953, Serial No. 383,812

Claims priority, application Great Britain October 3, 1952 3 Claims. (Cl. 253-78) This invention relates to turbo machines (turbines and axial flow compressors) having guide blades which are disposed between inner and outer annular members and are angularly adjustable about radial axes.

In some machines at least one of the annular members may not be rigidly secured to adjacent parts of the machine, either to allow for thermal distortions or because there are no suitable rigid and non-rotating parts in its vicinity to which it could be effectively secured. Nevertheless, accurate positioning of the annular members relative to each other is desirable. With fixed guide blades this presents no difliculty since the blades themselves provide an adequate rigid connection between the two annular members.

If the blades are to be angularly adjustable, however, they must be pivotally mounted in both the annular members with suflicient clearance to prevent binding, so that one annular member cannot be adequately supported by the other annular member through the medium of the adjustable guide blades. Nevertheless, accurate relative positioning of the members is still essential, for instance because the pivots for the adjustable guide blades should be kept in accurate radial alignment.

The problem of providing adequate mutual support for the annular members could be solved by fixing radial struts between them at intervals around the blade ring, but this solution has the disadvantage that the effective throat area of the blade ring is thereby significantly reduced. The present invention aims at providing a better solution to the problem.

Thus in a turbo machine according to the present invention a guide blade ring assembly comprises inner and outer annular members, angularly adjustable guide blades which extend between the annular members and are pivoted therein about radial axes, and non-adjustable guide blades interspersed at intervals between the adjustable guide blades and connected to both the annular members. Thus an annular member which is not otherwise rigidly secured in a particular direction in relation to the machine is supported against movement in this direction by the other annular member through the medium of the fixed blades. Accurate relative positioning of the annular members and alignment of the pivots of the adjustable blades is thus assured.

The fixed blades may be set at the correct angle for one operating condition of the turbo machine. Thus in this condition they will exert their full effect, while even in other operating conditions they will have some beneficial efiect and will be less obstructive than plain radial struts.

Conveniently the blade platforms are shaped so that in the extreme position-s of adjustment of the adjustable blades portions of the platforms come into contact with portions of the platforms of adjacent blades and so act as limiting stops.

In one form of the invention the outer annular member is fixed relatively to the casing of the machine but the inner annular member is not rigidly held except by the 7 2,917,275 Patented Dec. 15, 1959 ice non-adjustable blades. In this form of the invention, as applied for instance to a gas turbine power unit for aircraft, the inner annular member may comprise what is termed a balancing piston which is held against endwise movement in the machine and which supports at least a part of the axial thrust of the hot gases impinging upon the guide blades by receiving on its rear surface a gas pressure which substantially balances this part of the axial thrust and any other forces which tend to move it axially. In the case of a gas turbine power unit this gas pressure is conveniently derived from the compressor of the unit.

The outer ends of the non-adjustable guide blades may be connected to the outer annular member, for instance by links or slides, so that they can move radially relatively to the outer annular member to permit radial expansion and contraction of the blades but are restrained against axial movement. These blades will also serve to centralize the inner annular member.

One form of the invention as applied to a turbo-jet power unit for aircraft will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of the power unit;

Figure 2 is a cross-section taken on the line 11-11 in Figure 1, on a larger scale;

Figure 3 is a fragmentary longitudinal section taken on the line III-III in Figure 2, on a still larger scale; and

Figure 4 is a depeloped sectional view on the line IV-IV of Figure 2 showing the shape of the blade platforms of the adjustable blades.

The power unit shown in Figure 1 is of the type having an air compressor 10 at its forward end which discharges into an annular combustion chamber or into several individual combustion chambers 11 arranged side by side around the main axis of the power unit. The hot gases from the combustion chamber or chambers 11 pass through a ring of guide blades 12 and then through a turbine 13, finally being discharged to the atmosphere through a propulsionnozzle 14. The turbine 13 drives the compressor 10 through a hollow shaft 15 running lengthwise along the center line of the power unit.

The present invention is concerned with the ring of guide blades 12 arranged before the turbine 13.

The inner annular member of the ring of guide blades is a balancing piston 16 comprising an annular plate 17 having a shallow rearwardly directed flange 18 at its inner boundary and a deeper rearwardly directed flange 19 around its periphery. A disc 20 carried by the turbine shaft 15 runs within the inner flange 18 and actsas a seal, being spaced by a very small clearance from the inner flange 18. The balancing piston 16 is also connected to part of the wall or walls 21 of the combustion chamber or chambers 11 which wall or walls may undergo substantial relative thermal expansion in the axial direction, a sliding joint (not shown) being provided at some point to permit such expansion. In consequence of this sliding joint the said wall or walls 21 cannot hold the balancing piston 16 in the axial direction.

The guide blade ring must withstand the axial thrust of the hot gases impinging upon it, and in order to avoid having to take all this thrust through the outer ends of the blades 12, air under pressure is admitted to the rear surface of the balancing piston from the compressor 10 (Figure 1) through the shaft 15 and ports 22 and 23, which enables some of this thrust to be taken through the inner ends of the blades 12 by the balancing piston. The air pressure is also suflicient to balance any additional axial loads imparted to the balancing piston 16, for instance from the combustion chamber walls connected to it.

The fiange'19 around the periphery of the balancing piston supports the inner ends of the individual guide blades 12. The majority of these guide blades are pivotally mounted on this flange, each such blade having a spigot 24 which passes through a hole in the flange. The end of each spigot carries a crank lever 25, movement of which turns the blade angularly about a. radial axis. One way in which the crank levers for the adjustable blades may be moved is by an annular adjusting member 31 as described in the present applicants co-pending patent application, Serial No. 383,811, filed October 2, 1953, now abandoned.

At intervals around the peripheral flange 1.9 of the balancing piston 16 fixed blades 26 are provided which are rigidly secured to the flange, for instance by studs 27 at least one of which is threaded to receive a securing nut 28.

Around the outer ends of the blades is a shroud ring 29, which may if desired be made up of separate arcuate portions. The rear edge of this shroud ring abuts against an inwardly projecting annular shoulder of the casing 30 to provide a gas seal. Mounted in hearings in the casing 30 are spigots 32 (Figure 2) extending from the outer ends of the angularly adjustable blades 12. The spigots 32 can move radially in their bearings but are restrained thereby against axial and circumferential movement. The outer ends of the fixed blades 26, on the other hand, have spigots 33 which are connected to the casing 30 by links 34 disposed in a plane normal to the main axis of the power unit, such that the fixed blades 26 can expand and contract radially but arenot free to move axially relatively to the casing 30. Thus the casing 30 supports the balancing piston 16 concentrically with respect to the turbine shaft 15 through the medium of the fixed blades, and the balancing piston provides location in the radial sense for the inner ends of all the blades, the outer ends of which are free to expand and contract radially.

Conveniently the blade platforms 35 (Figure 4) are provided with stops 36 and 37 which, in the end positions of adjustment of the blades, come up against corresponding stops 38 and 39 on adjacent blade platforms, thus providing a positive limit to the angular adjustment of each blade.

What I claim as my invention and desire to secure by Letters Patent is:

1. An axial flow machine comprising a rotor, a casing, and a stator secured to said casing, a guide blade ring assembly including an inner annular member, and an outer annular member secured to said casing, angularly adjustable guide blades extending in a ring between said annular members, pivot means for said guide blades in said annular members aligned on axes radial to the axis of therotor, fixed guide blades arranged in the same ring expansion of said fixed blades, while coacting with said fixed blades to support said inner annular member relative to said outer annular member, said angularly adjustable guide blades being provided with non-circular platforms arranged at an equal distance from the rotary axis of the machine, the dimensions of the platforms being such in relation to the distance between adjacent blades axes that the parts of the platforms abut against each other in extreme positions of adjustment.

2. A turbine comprising a turbine rotor, a casing, and a turbine stator secured to said casing, a guide blade ring assembly disposed immediately upstream of said turbine rotor, and including an inner annular member, and an outer annular member secured to said casing, angularly adjustable guide blades extending in a ring between said annular members, pivot means for said guide blades in said annular members aligned on axes radial to the axis of the rotor, non-adjustable guide blades arranged substantially in the same ring and interspersed at intervals between said adjustable guide blades, said fixed guide blades rigidly interconnecting said annular members and substantially fixedly positioning said inner annular member within said casing, relatively angularly movable concentric walls extending between said turbine rotor and the inner annular member to set off a space. downstream of said inner annular member, gas-tight.

sealing means between said walls, and means for admitting to said space a gas under a pressure sumcient to produce a force on said annular member substantially to balance at least a part of the axial thrust exerted by the gas flow through said guide blade ring assembly.

3. A gas turbine as claimed in claim 2 in which both of said walls are of annular form, one being secured to said inner annular member and extending radially inwards therefrom, while the other is secured to the turbine rotor and rotates therewith, the gas-tight sealing means being of the rotary type.

References Cited in the file of this patent UNITED STATES PATENTS 

